Calcineurin (CaN) is a Ca - and calmodulin (CaM) binding protein first discovered in brain tissue in 1978 and subsequently found in many different tissue types. It is a hetero dimer composed of a large "A" subunit and a small "B" subunit. CaN-A is a class 2B protein phosphatase which contains an autoinhibitory region as well as separate domains for CaN-B and CaM binding. The discovery that CaN binds to immunosuppressive drug-immunophilin complexes implicated this enzyme as a central component of the immune response system. Both the A and the B subunits are required for CaN binding to such complexes and it has been shown that the activity of CaN and not other phosphatases in T-cells is inhibited by drug-immunophilin complexes. We wish to do data collection feasibility studies on CaN/imunophilin-drug complexes.